1. Field of the Invention:
The present invention relates to a front and rear wheel steering apparatus for steering both front and rear wheels of a motor vehicle, and more particularly to a front and rear wheel steering apparatus having a front wheel steering mechanism and a rear wheel steering mechanism which are mechanically operatively coupled to each other.
2. Description of the Relevant Art:
Front and rear wheel steering apparatus for motor vehicles are roughly classified into a group in which rear wheels are steered mechanically through a front wheel steering mechanism, and another group in which rear wheels are electrically steered independently of front wheels. The present invention is directed to a front and rear wheel steering apparatus belonging to the former class.
Typical mechanically operated front and rear wheel steering apparatus are disclosed in Japanese Laid-Open Patent Publications Nos. 58-30869 and 61-9378. The disclosed front and rear wheel steering apparatus has a front wheel steering mechanism and a rear wheel steering mechanism, the front wheel steering wheel mechanism being mechanically coupled to a steering wheel through a steering shaft and other members. The front and rear wheel steering mechanisms are mechanically coupled to each other by a shaft and other members for steering front and rear wheels.
In the conventional front and rear wheel steering apparatus, the steering wheel, the front wheel steering mechanism, and the rear wheel steering mechanism are mechanically coupled to uniquely determine the steering angle of the rear wheels dependent on the steering angle of the front wheels. Therefore, the cornering forces which the rear wheels produce during high-speed running of the motor vehicle, i.e., the steering characteristics of the motor vehicle, may not sufficiently reflect the steering intention of the driver of the motor vehicle or the conditions of the road on which the motor vehicle is running. As a result, the prior front and rear wheel steering apparatus tends to fail to fully have the benefit of its excellent steering characteristics.
Another problem is that if the ratio of front and rear steering angles is increased for higher maneuvering stability, then the motor vehicle develops an understeering tendency, making it difficult to turn the motor vehicle as desired.